A conventional rotation angle detector detects a rotation angle of a shaft of a motor or the like, for example, based on an output signal from a sensor element. Further, the conventional rotation angle detector checks whether the output signal from the sensor element has an abnormality, for example, as disclosed in JP 2005-49097A (EP 1503184 A2).
In the conventional rotation angle detector, output signals from a bridge circuit, that is, a +sine signal, a −sine signal, a +cosine signal, a −cosine signal are input to an AD conversion unit after differential amplification. Therefore, if one of those signals has an abnormality, the rotation angle cannot be calculated.
In addition, if an operational amplifier to amplify the output signals is short-circuited, for example, a mean value fixation abnormality, in which the output signal is persistently fixed to a mean value, which is an intermediate or means value of a maximum value and a minimum value of an amplitude of a normal output signal, may occur.